Constraint Effect on Fracture in Ductile-Brittle Transition Temperature Region

Abstract Bend fracture tests using flat plate specimens of 50mm thickness with a surface crack, 1TC(T), and SE(B) specimens of low alloy steel were performed in the ductile-brittle transition temperature (DBTT) region. Two types of SE(B) specimen, a/W = 0.1 and 0.5, were used. The fracture tests were conducted at −120°C and −80°C aiming at fracture mode of complete cleavage fracture at lower temperature and cleavage fracture after ductile crack growth at higher temperature. At −120°C, all specimens showed complete cleavage fracture. The shape factor of the Beremin model of the C(T) specimen or SE(B) specimen with a deep crack were determined by using each type of specimen at −80°C. Also, Toughness Scaling Model (TSM) was applied for determination of the Weibull parameters using two types of SE(B) specimens at −80°C. The GTN parameters were determined from fracture data of 1TC(T) specimen at the room temperature. The prediction analyses of the flat plate specimens for −120°C and −80°C were carried out using the Beremin model and the coupled model with the GTN model. The measured KJ of the tests for the flat plates were compared with the predicted KJ of 5% lower bound curve and 95% upper bound for the flat plate specimen which were deduced by the SE(B) specimen’s test data. Transferability from the test results of laboratory test specimens to that of a large specimen with low constraint, which was similar to the actual structure, was investigated. The temperature independency of the Weibull parameter m of the Beremin model was also confirmed.